This issue is more than likely due to a fairly recent update of the driver. I'm seeing the problem on all video ouput (mplayer, Flash plugin) regardless of type. 1080p50 (native) shows the issue much more than 1080p60 but is visible on both.

It looks like tearing but can only be described as a flickering box section of the image that is displaced. The box appears about a third of the way down the screen and is about 50pixels or so tall, extending 2/3 to the full width of the image. Is visible during movement.

I'm having trouble capturing a screenshot, capturing via mplayer is obviously too early in the display chain as the anomaly isn't visible in the shots. Any suggestions?

It's only apparent on HD video, vdpau or not. It's a flickery narrow band of about 10 pixels that extends from the left side to exactly the centre of the screen, about a 1/4 of the way down the screen from the top.

I think I have the same problem, however it's limited (not 100% sure about that) to external monitor (I'm using laptop). It even occurs when I move fast between still images so it's not restricted to videos, only fast movement.